Ampeg Scrambler - Surely this isn't working

Started by Rectangular, March 11, 2007, 09:08:40 PM

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Rectangular

hey all. I threw together an Ampeg scrambler as a quick evening build (tonepad's revolcador), but it doesn't seem to want to do anything

the problem I have with distortion/fuzz/etc circuits, is I can't really tell when they're working properly.  but given the sound samples I've heard of this thing, and all the positive response it gets around the forum, surely mine is wrong somehow... it just slightly boosts the signal, buzzes a bit, the texture control doesn't seem to do much, except it pops a bit of noise around 75% into the turn. should it be blatantly obvious when its on ? does this thing spew noise ?

using MPSA14 for the darlingtons, and I've tried BC169s and 3904s for the NPN, but no change. I can't understand how a circuit this simple doesn't work

also I'm aware of the tonepad error with the reversed electrolytic (C3). are there perhaps other errors ? would anyone be willing to check the voltages of their working build ? tried putting in those optional diodes...nothing. I went through it with an audioprobe, all the trannies seem to be doing their thing, but at no point does the signal get really extreme/noisey

rec

sfr

It should be pretty darn obvious when the thing is on. I'd suggest checking the wiring to the "blend" control - in one direction, you should get nothing but clean signal coming out, but audio probing as you've done, you should here a pretty distorted signal coming out of the thing just prior to the blend pot - even with texture all the way down, it's still pretty fuzzy on mine, just not end-of-the-world octave fuzz. 

sent from my orbital space station.

tcobretti

This thread has some sound clips of me turning the blend pot with a footpedal while I play.

http://www.diystompboxes.com/smfforum/index.php?topic=48637.0

Rectangular

hey guys, thanks for the feedback. I'm starting to suspect these darlingtons. I don't know what a high-gain darlington is supposed to sound like, but I'm not getting much of a boost from these MPSA14s... Ill see if I can find 2n5306s anywhere. so far,  the bc169 is the only thing in here that's blaring

rec

tcobretti


Rectangular

are those a13's loud ? because even the initial gain stage on mine, the first darlington, it doesn't seem to really boost anything. I've tried every pin swap/combination possible and got nothing

tcobretti

I haven't audio probed it, but the 13s are VERY high HFE.